1. Thorpe, W. H., Learning and Instinct in Animals, second ed., 464 (Methuen, London, 1963).
2. Andrew, R. J., Science, 137, 585 (1962).
3. Lilly, J. C., Proc. Amer. Phil. Soc., 106, 520 (1962).
4. Konorski, J., Rozprawy Wydziatre Nauk Medycznych (Warsaw) R, 6–T 2, 11–32 (1963) (in Polish with summaries in Russian and English).
5. Lade, B. I., and Thorpe, W. H., Nature, 202, 366 (1964).